Line piecrust with parchment paper or aluminum foil; fill piecrust with pie weights or dried beans.

Bake at 400 for 10 minutes. Remove weights and parchment paper; bake 5 more minutes, and set aside. Reduce oven temperature to 350.

Cook bacon in a large skillet over medium high heat until crisp. Remove bacon, and drain on paper towels, reserving 2 t. drippings in pan. Crumble bacon and set aside.

Saute chopped onion and mushrooms in hot drippings 3 to 4 minutes or until tender.

Stir together bacon, onion mixture, half and half, and next 4 ingredients in a large bowl. Combine cheese and flour; add to bacon mixture, stirring until blended. Pour mixture into crust.

Bake at 350 for 45 to 50 minutes or until a wooden pick inserted in center comes out clean. Shield edges with aluminum foil to prevent excess browning, if necessary. Let stand 10 minutes before serving.